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Date: Wed, 4 Mar 2009 22:14:09 +0100
From: Luigi Rizzo <rizzo@iet.unipi.it>
To: Sebastian Mellmann <sebastian.mellmann@net.t-labs.tu-berlin.de>
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Cc: freebsd-ipfw@freebsd.org
Subject: Re: ipfw (dummynet) adds delay, but not configured to do so
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On Wed, Mar 04, 2009 at 10:05:53PM +0100, Sebastian Mellmann wrote:
> 
> > On Wed, Mar 04, 2009 at 08:17:05PM +0100, Sebastian Mellmann wrote:
> >   
> >> Hi everyone!
> >>
> >> I hope this is the right place to ask.
> >>
> >> I've got a IPFW ruleset that looks like this:
> >>
> >> cmd=ipfw
> >> bottleneck_bandwidth=100Mbit/s
> >> in_if="em0"
> >>
> >> $cmd pipe 500 config bw $bottleneck_bandwidth
> >> $cmd add pipe 500 all from any to any via $in_if
> >>     
> >
> > the delay that a packet experiences corresponds to len/bandwidth,
> > often rounded up to the next clock tick (1ms is the default).
> > You get one delay inbound, one delay outbound, so that's 2ms.
> >
> >   
> Is there any chance to change this clock tick to a lower value?
> I think it's the 'HZ=' option in the kernel config isn't it?

yes. i believe there is a tunable (so you don't need to rebuild
the kernel) but i do not remember exactly which one.

cheers
luigi